cut the opening on a 45 degree angle and caulk in drain
First determine what you are going to install as the shower unit. If there is to be no shower unit and it will just drain through the concrete floor, then it will be flush with the floor. If you are installing a unit, then you need to look at the unit to determine the distance obove the concrete to place the drain.
If you have a drain available. You may need to chip some concrete around the drain to install the bottom half of the drain. With that in place, set the shower over it and the top piece screws into the drain to form a seal. You can build a 2x4 frame and raise the shower up enough to run a drain to a sump or a floor drain.
You need at least a 3 in. pipe -- shower is 2 in. pipe
With a compression mission ring
see this link for one answer http://www.oatey.com/shower_drains/lit/Shower%20Pan%20Liner.pdf
If you reduce the soil connection to 2" and install a trap
A shower drain is 1 1/2 or 2 inch and a toilet needs to be either 3 or 4 inch.
Shower drain goes into a trap under shower. Continue piping from trap to drain line.
The flange connects to the shower and just goes through the floor. It shouldn't mount to the floor.
Water won't drain from shower. Either trap or shower drain line is clogged.
How to Install Mortar Shower Pan Membrane LinerOnce you've framed the shower stall, it is time to install the pan liner and cement backer board to create a water tight seal.Remove the drain cap and tape over the drain to keep mortar and other debris from entering the drain. Put down a layer of felt paper to help prevent moisture from wicking down through to the subfloor. Place a layer of metal lathe over the felt paper. Trowel in a layer of mortar that it has a one quarter inch slope towards the drain. Once the mortar dries, place a layer of felt paper along the walls of the shower stall. Attach cement board with the rough side out along the top half of the walls. Install the shower stall membrane in the bottom of the shower so that it overlaps in the corners, covers the shower curb and is approximately six inches up the side of the walls. Cut out holes for the drain, the drain bolts and the weep holes. Seal the underside of the membrane near the drain with silicone. Nail the membrane that covers the curb only on the outside. Attach the remaining cement board leaving one inch clearance from the bottom. Caulk all seems. Place some pebbles near the weep holes to protect the openings. Trowel in a layer of mortar that has a one quarter inch slope towards the drain. Mortar the curb. Remove the tape from the drain.
$8,300